There is no “one size fits all” where the gullet channel of your horse’s saddle is concerned. The width of each horse’s spine will determine how wide this must be.
Calculate how wide your horse’s spine is by standing on your horse’s left side and placing your hands on his spine in the saddle support area. With the tips of your fingers, gently palpate downward towards the ground. You will feel bone (transverse processes of the lumbar vertebrae), then a slight rigidity (supraspinal ligament), and finally, a soft area (back muscle or longissimus dorsi). Mark the start of this muscle and then do the same thing on the other side. Take your hand and make a bridge over your horse’s back from mark to mark. The number of fingers you can get inside your bridged hand will determine the width of the gullet required.
The width of the gullet must be the same from pommel to cantle. We see saddles with gullets that are the appropriate width at the front, but then get narrower towards the back. The result is 4-5 fingers gullet width under the pommel, but only 2-3 fingers at the cantle (or less). This makes no sense. The horse’s spine and surrounding ligaments do not get narrower over the length of his saddle-support area.
A saddle that is too wide through the gullet will have an inadequate weight-bearing surface, may start to strip muscle away from the top of the ribs, and the back of the tree may actually rest on the spine.
A much more common problem is a saddle with too narrow a gullet. This saddle will sit on the horse’s spine and/or ligaments. This is especially noticeable when the horse goes around a corner: when tracking to the left, you will see the saddle shift to the right, so that the left-side panel rests on the horse’s spine/ligaments. This will cause a tightening of the back muscles and hollowing the back; exactly the opposite of the nice rounded back that we want. In the long-term, a saddle with too narrow a gullet causes permanent, irreversible back damage – most severely: spinal stenosis (compression and narrowing of the spinal canal) and spondylosis (degeneration of the vertebrae).
Author of ‘Suffering in Silence - The Saddle fit Link to Physical and Psychological Trauma in Horses’ (2013) Jochen Schleeseteaches riders and professionals to recognize saddle fit issues in Saddlefit 4 Life lectures and seminars. We help you find answers in a personal 80 point Saddle Fit Diagnostic Evaluation.